Jubilee

Mine looses prime all the time. I have to rev the engine to get it to go. Sometimes pointing it down hill works too.

Fessman

If and when the unloading valve stops moving then the lift won't lift until the problem that is causing this condition is fixed.

A faulty back pressure valve can cause the unloading valve to stick.

The unloading valve can stick on it's own.

The unloading valve has an O ring that can become worn until it will not allow the valve to move.

The pump could have lost it's prime too. The piston pump must be bled by opening the front head plug in the pump and running the engine slowly until all air bubbles are gone from the escaping oil. Stop the engine, replace the plug and start the engine again to see if that fixes the problem. It can!

If the touch control is in the down position, then this is what should happen, whether the tractor is running or not.

If the touch control is in the up position with the tractor running, and the 3 point lift won't raise, the most likely culprit is that the front hydraulic pump has lost prime. The easiest way to restore prime is to pressurize the transmission using shop air and a rubber-tipped air gun (while the tractor continues to run). The dipstick is a convenient place to apply such air. Don't over-do it -- 5 PSI (i.e. a quick shot of air) is usually enough.